In the processing industries, it is customary to blend fluid and semi-fluid materials under pressure by passing them through a continuous mixer which includes a mixing head. This mixing head includes a rotor member having a plurality of teeth extending outwardly from its outer surface. A stator member is disposed about the rotor member and includes circumferentially disposed rows of teeth which are arranged to interdigitate with the rotor teeth. Material is inserted into the mixer under pressure and passes between the interdigitated teeth of the rotor and stator causing it to be beaten and mixed.
In prior art apparatus of this type the rotor was a disc having circumferential rings of teeth extending outwardly from its opposed surfaces. The stator in turn surrounded the rotor and included two members with substantially planar stator surfaces having circumferential rings of stator teeth mounted thereon which intermesh with the rotor teeth on each of the opposed rotor surfaces. The planar type stator members used in this prior art apparatus had to be made relatively thick and therefore heavy in order to withstand the substantial forces generated during mixing since unlike the rotor member forces on the stator members are unbalanced. In addition the disc shaped rotor used in such a configuration was a solid member making it difficult to dissipate the undesirable heat resulting from the mixing operation, which if not adequately dissipated requires additional processing steps and added cost.
In an attempt to avoid the above described disadvantages rotors have been designed in a cylindrical configuration with teeth extending radially outwardly from the cylindrical surface. The stator of such a mixing head is a hollow cylinder with inwardly extending teeth which are again arranged to interdigitate with the outwardly extending rotor teeth. Such a mixing head has advantages from the standpoint of reduced stator weight and improved heat dissipation but has mechanical disadvantages; since only one surface on each of the rotor and stator are available for mixing teeth. In general, since it is advantageous to have as many mixing teeth as possible, the cylindrical head must be made undesirably long to provide adequate surface area for teeth. In addition it is mechanically convenient to have the material enter the head along the rotor shaft and with the cylindrical type of rotor, means must be provided to insure that this material is substantially equally distributed about the cylindrical rotor surface.
The teeth of prior art mixing heads were substantially rectangular in configuration and were substantially identical in shape at all points on both the rotor and stator surfaces. Material entering the mixing head of a mixer utilizing such prior art teeth tended to remain axially stratified as it passed between the rotor and the stator because insufficient mixing occurred in an axial direction which is the direction extending along the projecting teeth. It is also necessary to provide teeth having an adequate cross sectional area in order to make them strong enough to withstand periodic impact forces which are generated during disassembly of the head for cleaning and maintenance and which can result when hard pieces of foreign material are within the material to be mixed. Providing rectangular teeth having the minimum cross sectional area needed to provide this strength would limit the number of teeth which could be provided on the available rotor and stator surfaces. As indicated above it is advantageous to provide a maximum number of teeth per unit area on these surfaces to insure the best mixing characteristics of the resulting mixing head.
Applicant has solved the above described problems by providing a mixing head having a conically shaped rotor and stator members and teeth with a unique, tapered configuration. The conical stator provides a saving in weight over planar type stators while still providing a component of superior strength. The conical rotor may be conveniently made hollow to provide a cavity which may be utilized for a circulating coolant if desired to improve the heat dissipation of the head. The novel tooth configuration disclosed provides a maximum packing density of teeth on the available rotor and stator surfaces while providing strong teeth which resist breakage. The inventive tooth configuration also provides superior mixing in an axial direction along the projecting teeth. Larger heavier teeth of special shape are also provided in the area where the material enters the head. These larger teeth provide increased radial mixing in this area and provide greater resistance to breakage by foreign material introduced into the head.